The present invention relates to monolithic vibration damping materials comprising a polymer. The invention further relates to data storage medium prepared from the vibration damping materials.
Vibration damping is a common need in many mechanical systems where undesired resonances may be excited by normal perturbations. The suspension system in an automobile, for example, will exhibit large unwanted oscillations in response to road irregularities unless properly damped. Vibration dampers used in automobiles consist of springs providing shock and vibration isolation to a motor vehicle seat assembly.
Layers of elastomeric materials that absorb energy are other types of damping material. Polyethylene, polypropylene, non conjugated dienes, rubber cross linkers and similar materials are used in these vibration systems. Composites of metal and polymer are employed on the outside of many computer hard disk drives to reduce the noise of the drive within the computer. Vibration dampers are also used in printed circuit boards and spindle motors in internal disk drive applications. In particular, vibration damping materials are used to guard the interior of a disk drive from external shock forces.
Materials used for vibration damping should exhibit large viscous losses in response to deformation. These losses are typically quantified in terms of either dynamic Young""s moduli or dynamic shear moduli. In either case, the dynamic storage modulus, by definition, is proportional to the amplitude of the stress which results in response to a sinusoidal strain applied in phase with the stress (where the strain may be either shear or elongational depending on whether shear or Young""s modulus is desired respectively). Similarly, the loss modulus is, by definition, proportional to the amplitude of the stress which results in response to the application of a sinusoidal strain rate applied out of phase with the stress. The ratio of dynamic shear loss modulus to dynamic shear storage modulus, or dynamic Young""s loss modulus to dynamic Young""s storage modulus, at a particular oscillation frequency, is commonly referred to as tan xcex4. The magnitude of the loss modulus in a material quantifies its viscous-like resistance to deformation while tan xcex4 quantifies the relative magnitude of this resistance to elastic response.
Due to a wide range of possible applications, there has been an intense research in polymer systems capable of damping out vibrations. Most polymer systems have a low fundamental vibration frequency. Many of these systems employ an elastomer in combination with a glassy polymer, metal, or combination thereof which are in contrast to single phase homogenous materials, i.e. monolithic systems. Monolithic polymers have the advantage of better surface smoothness. Thus, it would be desirable to develop damping systems which offer damping at room temperature without the use of a dispersed rubbery phase or blocky copolymer. xe2x80x9cBlocky copolymerxe2x80x9d as used herein refers to multiple phase polymer systems with alternating monomer sequences that may be of varying length.
One area in which there has been intense research in polymer systems capable of damping out vibrations is in xe2x80x9cfirst surfacexe2x80x9d medium. Unlike compact disks (CD) and digital video disks (DVD), storage medium having high areal density capabilities, typically greater than 5 Gigabits per square inch, employ first surface or near field read/write techniques in order to increase the areal density. xe2x80x9cFirst surfacexe2x80x9d as used herein refers to the data layer which is on the surface of a substrate wherein an optic does not pass through the substrate. xe2x80x9cNear field read/write techniquesxe2x80x9d as used herein refers to an optical mechanism wherein the number aperture is greater than about 0.08. For such storage medium, although the optical quality is not relevant, the physical and mechanical properties of the substrate become increasingly important. For high areal density applications, including first surface applications, the surface quality of the storage medium can affect the accuracy of the reading device, the ability to store data, and replication qualities of the substrate. Furthermore, the physical characteristics of the storage medium when in use can also affect the ability to store and retrieve data. For instance, if the axial displacement of the medium is too great, the axial displacement can inhibit the accurate retrieval of data and/or damage the read/write device. Thus, improved vibration performance may be achieved by either high modulus or high damping.
Conventionally, the issues described above in substrate have been addressed by utilizing metal, for example, aluminum, and glass substrates. These substrates are formed into a disk and the desired layers are disposed upon the substrate by various techniques.
Vibration concerns and high axial displacement are critical in the design of data storage devices, such as optical disk drives and hard disk drives. It would also be desirable to develop damping systems utilizing monolithic polymers which are suitable for use in data storage devices, in particular in substrate applications.
The present invention provides a storage medium for data, the storage medium comprising:
1) a substrate comprising at least one polycarbonate portion, and
2) at least one data layer on the substrate;
the polycarbonate comprising at least one compound of structure (I), (IV), or combinations thereof: 
xe2x80x83where
R1, R2, R3, R4, R5, and R6 are independently selected from the group consisting of C1-C6 alkyl and hydrogen;
R7 and R8 are independently selected from the group consisting of C1-C6 alkyl, phenyl, C1-C6 alkyl substituted phenyl, or hydrogen;
m is an integer in a range between 0 and about 12;
q is an integer in a range between 0 and about 12;
m+q is an integer in a range between about 4 and about 12;
n is an integer equal to 1 or 2; and
p is an integer equal to 1 or 2.
The present invention further provides a polycarbonate composition with improved damping performance which comprises at least one compound of structure (I), (IV), or combinations thereof.
The present invention further provides a method for improving the damping performance of an article, the method comprising constructing the article of a polycarbonate with at least one compound of structure (I), (IV), or combinations thereof.